The present disclosure relates to an imaging lens that has a focusing function and is suitably used in an electronic camera such as a digital video camcorder and a digital still camera. The present disclosure also relates to an image pickup apparatus that uses such an imaging lens.
Recently, a digital video camcorder, a digital still camera, etc. that use a solid-state image pickup device such as a CCD (Charge Coupled Device) and a CMOS (Complementary Metal-Oxide Semiconductor) have been rapidly in wide spread use. Due to the spread of such digital cameras etc., a demand has been increased for a high-performance imaging lens that has superior portability and is suitable for high pixel density. Moreover, recent needs are various, which can be seen from some users requiring not only a zoom lens but also a single-focus lens that has a fixed focal length.
As a need for the single-focus lens, the single-focus lens is expected to have a half angle of view covering a wide angle around 30 degrees, a large aperture ratio having an open F number of about F2, compact size, and high performance. As such an imaging lens, a retrofocus-type imaging lens is known. However, the retrofocus-type imaging lens tends to have long total optical length (for example, see Japanese Unexamined Patent Application Publication No. 2010-39088). On the other hand, Japanese Unexamined Patent Application Publication Nos. 2011-64919 (JP2011-64919A) and 2012-63676 (JP2012-63676A) disclose an imaging lens that is intended to reduce size by adopting telephoto type. An imaging lens disclosed in JP2011-64919A includes a negative lens group, a positive lens group, a positive lens group, and a negative lens group that are arranged in order from object plane, and has a half angle of view of about 25 degrees and an open F number around 2.8. An imaging lens disclosed in JP2012-63676A includes a positive lens group, a positive lens group, and a negative lens group that are arranged in order from object plane, and has a half angle of view of about 30 degrees and an open F number around 2.0.